Method and device for the measurement of off-center rotating components

ABSTRACT

An apparatus and a method are presented in order to carry out an automatic optical inspection of an off-center rotating component to be measured. Using a measurement procedure which avoids mechanical contact having a source producing parallel rays and a detecting means, the off-center rotating component is rotated about a rotational axis, whereby a motion of the detecting means is synchronized with the rotation and is carried out in such a fashion that the separation, in the direction of an optical axis, between the off-center rotating component and the detecting means remains constant. In this manner optical distortions are avoided which would otherwise occur in the optical measurement procedure.

BACKGROUND OF THE INVENTION

The invention concerns a method for the measurement of off-centerrotating components of a measured object, whereby the measured object issupported in a rotatable fashion and rotates about a rotational axis anda measurement plane is defined perpendicular to the rotational axiswithin which the part of the measured object to be measured isirradiated with a parallel beam emanating from a radiative source, andhaving a detecting means for recording the silhouette of a cross sectionthrough the measured object in the measurement plane produced by theradiative source and the measured object, as well as an apparatus forcarrying out the method.

An apparatus and a method of this kind have become known in the art bymeans of the international publication WO86/07442.

The method and apparatus which are known in the art are suitable fordetermining the dimensions of an elongated measured object. An opticalelectronic measuring station is proposed for the automatic dimensionalcontrol of outer rotating components by means of which the object to bemeasured is illuminated from below by an linear radiative source inorder to produce an image of two diametrically opposed contour points ontwo linear photodiode arrays. The resulting intensity discontinuitiesgive the two contour points and the shaft diameter can be determined bythe electronically recorded separation between the two diode cells.

FIG. 1 shows the fundamental principle of the measurement in accordancewith prior art. A radiative source 1 produces a beam 22 comprisingparallel rays which illuminates an object to be measured 2 along anoptical axis 8. The elongated measured object 2 rotates about arotational axis which runs through the center 7 perpendicular to theplane of the drawing. A detecting means 3 comprises two separateddetector elements 5, 5' whose separation with respect to each other ismovable by means of a positioning means 4. Since the beam 22 comprisesparallel rays, the position of the beam on the detector 5 produces asilhouette having an intensity profile. The sampled change in theintensity in the vicinity of the edge of the measured object allows, inconcert with the electronically determined separation between the twodetector linear photocell arrays 5, 5', for a precise dimensionalmeasurement of the measured object. A repeated measurement of thediameter during the rotation facilitates a determination of theroundness of the measured object. With an apparatus in accordance withprior art the resolution for the diameter measurement assumes a value ofone micron and the longitudinal precision assumes a value of 0.002 mm.With this apparatus it is possible to measure shafts in the diameterrange from 7 to 100 mm having a length from 200 to 700 mm.

Although the measured diameters and roundnesses can be determined quiteprecisely, the apparatus and the method in accordance with prior arthave the disadvantage that asymmetric measured components can not bemeasured to the required precision, since the rotation of such acomponent leads to errors in the measurement.

It is therefore the purpose of the present invention to improve anapparatus and a method of the above mentioned kind in such a fashionthat rotating components having an asymmetric stroke support positioncan be measured sufficiently accurately.

SUMMARY OF THE INVENTION

This purpose is achieved in accordance with the method of the inventionin that the rotational axis position is adjusted between the detectingmeans and the beam in such a fashion that the off-center rotatingcomponent which is to be measured is illuminated and initially, with astationary detecting means, the maximum excursion of a diameter of theoff-center rotating component is determined by means of a silhouetteprojection onto the detecting means, an angle of rotation of theoff-center rotating component is determined, and the detecting means issynchronized with the position of the angle of rotation and movedparallel to the beam in such a fashion that the separation, parallel tothe beam, between the detecting means and the rotating off-centercomponent is kept constant.

The purpose of the invention is likewise realized by means of anapparatus for carrying out the method which exhibits: means forpositioning the measurement plane so that it intersects the off-centerrotating component to be measured, an angle measuring device todetermine an angle of rotation of the off-center rotating component, astroke means, which is configured in such a fashion that it can move thedetecting means parallel to the beam, a synchronizer which synchronizesthe stroke motion of the detecting means with the angular position ofthe off-center component and a computer to store, control and evaluate,whereby the detecting means are moved in such a fashion that theseparation parallel to the beam, between the detecting means and therotating off-center component is kept constant.

In this fashion the purpose of the invention is achieved. By means of adetermination of the angular position of the rotating off-centercomponent and by means of a synchronization of this angular positionwith a position of the detecting means movable parallel to the beamdirection, the above mentioned measurement errors due to the changeablepositions within the measuring optics can be avoided. During therotation, an arbitrary point on the off-center rotating component to bemeasured exhibiting a given constant separation from the rotational axisdescribes a sinus-shaped motion relative to the optical axis whilerotating in a circle about an off-center rotational axis. By means of acorresponding sinus-shaped motion of the detecting means relative to therotational component, it is possible to maintain its separation,parallel to the beam, from the off-center rotational axis. By means ofthe measurement of the off-center rotating component at various angularpositions during the rotation, it is possible for differing silhouetteprojections to be recorded, whereby the roundness of the off-centerrotating component can also be determined.

It is particularly advantageous when the method is utilized to measurecrank shafts. Such an application has the advantage that precisionmeasurements of crank shafts can also be carried out automaticallywithout mechanical contact.

It is also advantageous when the method is carried out to measure crankshafts having a plurality of off-center rotating components with aplurality of angles of rotation relative to each other. A utilization ofthe measurement procedure for the measurement of crank shafts of thiskind has the advantage that even crank shafts having a complicatedcomposition of off-center rotating components and exhibiting variousangular positions with respect to each other can be measuredautomatically and without mechanical contact.

A particularly advantageous embodiment of the apparatus for carrying outthe method utilizes two linear photodiode arrays to measure theoff-center rotating component. This embodiment has the advantage thatthe advanced technology of CCD-cameras and laser scanners can be takenadvantage of, whereby a plurality of individual measurements perrotation can be carried out.

In a variation of this embodiment, the apparatus exhibits a positioningmeans in order to adjust the separation between the two linearphotodiode arrays. This variation has the advantage that even off-centerrotating components with very differing diameters can be measuredthrough the utilization of two adjustable linear photodiode arrays.

An advantageous embodiment of the apparatus for carrying out the methodexhibits a positioning device in order to position the detectorstransverse to the beam. This embodiment has the advantage that differingedges of the rotating off-center component can be detected at differingangles of rotation during the rotation so that the roundness of theoff-center rotating component can also be determined.

Further advantages can be derived from the description and theaccompanying drawings. The various features which are to be describedcan be utilized in other embodiments either individually or in arbitrarycombination.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a brief description of the measurement principle inaccordance with prior art;

FIG. 2a shows a cross section in a plane perpendicular to rotationalaxis of an off-center rotating component to be measured;

FIG. 2b shows a side view of the rotating component to be measured ofFIG. 2a with accompanying rotation and detection components;

FIG. 3a shows a side view in the measurement plane where the off-centercomponent to be measured lies on the optical axis at maximum separationfrom the radiative source;

FIG. 3b shows a representation of the measurement configuration for thecase where the off-center component to be measured assumes an angle of90° relative of that of FIG. 3a during rotation;

FIG. 3c corresponds to the configuration of FIGS. 3a and 3b but for thecase where the off-center rotating component to be measured is on theoptical axis and as close as possible to the source;

FIG. 4 shows a schematic representation of the connections betweencontrol components and the synchronized components in accordance withthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 describes the fundamental principle of the measurement inaccordance with prior art. A radiative source 1 produces a largelyparallel beam 22 which irradiates an object 2 to be measured in such afashion that a silhouette is created on a detecting means 3 equippedwith a detector 5, 5'. The vertical position of the detector 5, 5' aswell as the separation between possible detector portions 5, 5' isadjusted by means of a transverse positioning means 4.

The roundness of the measured object 2 can be determined by a rotationof the measured object 2 about a rotational axis which runsperpendicular to the plane of the drawing through the rotation center 7together with an analysis of the intensity discontinuities in detector5, 5'. An optical axis 8 defines the parallel travel direction of thebeam through the rotation center 7. A transverse axis 6 cuts the opticalaxis 8 in a perpendicular direction through the rotation center 7.

Although, due to the parallel optical path of the beam 22, the measuredresults, for example with regard to the diameter of the measured object2, are largely insensitive to small displacements in the direction ofthe optical axis, large displacements of the measured object along theoptical axis cause optical distortions which falsify or degrade themeasured results. Consequently, when executing a measurement of ameasured object having a off-center rotating component, it is initiallynot possible to carry out a precise measurement of the off-centerrotating component without undertaking additional measures.

FIG. 2a shows a cut in the measurement plane corresponding to the planeof the drawing of FIG. 1 of an object to be measured 2 having anoff-center rotating component. The off-center rotating component 10rotates, in this embodiment, about the rotation center 7 on anoff-center stroke circle 13. In many cases, for example in the case of acrank shaft, a point 11 on the edge of the off-center rotating componentalso describes a circular motion about the rotation center 7 during therotation of the measured object. In this fashion the off-centeredrotating component also exhibits its own off-center rotation center 12which, for its part, describes an off-center stroke circle 13 about therotation center 7. During the rotation the off-center rotation center 12exhibits a changing angle a relative to the transverse axis 6 which, forits part, is perpendicular to the optical axis 8.

FIG. 2b shows a side view of the apparatus. The measured object 2 issupported in a rotatable fashion between rotation means 15 in such amanner that a rotation in the rotation direction 16 about the rotationalaxis 18 is carried out. During the rotation the off-center rotationalaxis 19 and the off-center component 10 describe a cylindrical motionabout the rotational axis 18 so that a cylinder-shaped surface isswept-out during a rotation of the off-center component. An opticalhousing 9 is arranged in the vicinity of the off-center component 10 insuch a fashion that a precise measurement of the diameter or theroundness of the off-center rotating component 10 can be carried out. Arotational axis positioning means 21 adjusts the position of the opticalhousing 9 along the rotational axis 18. An angle measuring device 14 isarranged in such a fashion that the angular position or the angle ofrotation α of the rotating off-center component is recorded in realtime. The measuring plane 17, in which the cross sections according toFIGS. 2a, 3a, 3b and 3c lie, is indicated in FIG. 2b.

In the event that a measurement is carried out in the measurement plane17 the following steps are executed in accordance with FIGS. 3a, 3b, 3c.FIG. 3a shows the contents of the optical housing 9 having a radiativesource 1 which produces the parallel beam 22. During the rotation of themeasured object, the off-center component 10 describes an off-centerstroke circle 13 about the rotation center 7, whereby a separation d,parallel to the optical axis 8, obtains between the off-center rotationcenter 12 and the detector 5, 5'. The rotating off-center rotationcenter 12 is, in FIG. 3a, located precisely on the optical axis 8. Viathe transverse positioning means 4 the detectors 5, 5' of the detectingmeans 3 are positioned in such a fashion that the silhouette of theoff-center component 10 which is produced by the projection of the beam22 is recorded with the detectors 5, 5'. The detectors 5, 5' aresuitable for detecting the radiation from the radiative source 1 and theintensity profile of the silhouette. The intensity measurements of thedetector in the shadow of the off-center component 10 are, with theexception of a possible small background, zero. Outside of the shadowthe intensity naturally corresponds to the complete intensity of thesource. Consequently, a sharp intensity profile change occurs preciselyat that position where the projection of the edge of the measured objectonto the detector plane 5, 5' is produced. The separation d is adjustedby means of a stroke means 20 which will be further described below.

During the rotation the position of the off-center component moves, forexample, into the position shown in FIG. 3b. In FIG. 3b the rotatingoff-center component 10 is precisely in the vertical position, e.g. theoff-center center 12 lies on the transverse axis 6. If then, via thetransverse positioning means 4, the detectors 5, 5' of the detectingmeans 3 are adjusted in such a fashion that the sharp intensity changeof the silhouette can be detected, a silhouette profile corresponding tothe diameter of the measured object is imaged on the detector 5, 5'. Theangular position a between the off-center center 12 and the transverseaxis 6 (see FIG. 2a) then has, in this position, a value α=0 and,consequently, the off-center rotating component 10 has moved in thedirection towards the radiative source 1. Stroke means 20 is, however,adjusted accordingly so that the detecting means are displaced towardsthe radiative source in such a fashion that the separation d ismaintained or kept constant. In this manner optical distortions due to achanging separation between the detector and the off-center component tobe measured are avoided.

If one continues to rotate further in accordance with FIG. 3c, then theoff-center component 10 is located in a position having an angle ofrotation α=270°. The stroke means 20 displaces the position of thedetecting means 3 towards the source in such a fashion that theseparation d between the off-center rotation center 12 and the detector5 remains constant. In the event that detector configuration 5, 5' ischanged via the transverse positioning means 4 in such a fashion thatthe silhouette of the off-center component can be detected, a measuringresult in accordance with FIG. 3c can be utilized, in combination withFIG. 3a and 3b, to record three diameter measurements of the off-centercomponent 10 and to thereby check the roundness or the eccentricity. Thetransverse positioning means 4 is also suitable for changing theseparation between the two detector parts, for example 5, 5', so thatobjects of most differing diameters can also be measured.

FIG. 4 shows a schematic diagram of the cooperation and control betweenthe differing components of the system. The synchronizer 30 is connectedby means of conductor 47 to the rotation means 15 as well as to theangle measuring device 14 via conductor 43. A connection 44 between thesynchronizer 30 and the stroke means 20 allows for the stroke means 20to be adjusted in such a fashion that the separation parallel to theoptical axis 8 between the off-center rotating component and thedetecting means is kept constant. The position of the angle of rotationis detected by means of the angle measuring device 14. Additionalconnections 45 and 42 are shown in FIG. 4 between the synchronizer thetransverse positioning means 4, and the computer 40, respectively.Connection 45 facilitates a synchronization of the transversepositioning means 4 with the angle measuring device 14 so that a motionperpendicular to the optical axis, e.g. parallel to axis 6, can also besynchronized with the rotation of the off-center rotating component.Synchronization information is stored via conductor 42 and computer 40.Computer 40 stores, controls and evaluates information. The angle ofrotation position a is stored via conductor 41 and the intensity profileof the silhouette detected by detector 5, 5' is read out or stored viaconductor 46 or 46'. Clearly, additional conventional connectionsbetween the computer 40 and the various components of the system inaccordance with FIGS. 2 through 3c are possible in order to effect anautomatization of the measuring process.

It is possible, with the method and apparatus in accordance with theinvention, to monitor diameters and to measure diameters with aprecision of approximately 1 micron. Measurements of this type can, forexample, be carried out on measured objects having lengths between 0 and3000 mm and having diameters between 0 and 1000 mm. Measurement ofoff-center rotating components can be carried out on, for example, crankshafts. The detecting means 5, 5' can have photocells connected to anoptical CCD camera or a laser scanner. With a pixel read-out frequencyof, for example, 10 MHz, a sample frequency of 5 KHz is to be expected.With a measured object rotational frequency of 1 Hz, 5000 samples perrotation are possible. Stroke throws of the off-center rotatingcomponent of, for example, ±200 mm can be measured with this method andwith this apparatus.

We claim:
 1. A method for measurement of an off-center rotatingcomponent of a measured object comprising:supporting the measured objectfor rotation about a rotation axis; illuminating the measured objectwith a parallel beam from a radiation source within a measurement planeperpendicular to said rotation axis; detecting, using detecting means, asilhouette of a cross section through the measured object; determining aposition of said rotation axis relative to said detecting means;adjusting said measurement plane to intersect the off-center rotatingcomponent; measuring, with stationary detecting means, a maximumexcursion of a diameter of the off-center rotating component; observingan angle of rotation of the off-center rotating component; and movingsaid detecting means parallel to said beam to keep a constantseparation, parallel to said beam, between said detecting means and saidoff-center rotating component.
 2. The method of claim 1, wherein themeasured object is a crank shaft.
 3. The method of claim 2, wherein saidcrank shaft comprises a plurality of off-center rotating componentshaving a plurality of relative angles of rotation.
 4. An apparatus formeasurement of an off-center rotating component of a measured objectcomprising:a rotatable support device for supporting the measured objectin a rotatable fashion,; means for defining a measurement planeperpendicular to a rotational axis; a radiative source producing aparallel beam in said measurement plane; a detecting means arranged fordetecting a silhouette of a cross section of the measured objectproduced by said beam and the measured object; means for positioningsaid measurement plane to intersect the off-center rotating component;an angle measuring device for determining an angle of rotation of theoff-center component; a stroke means for moving said detecting meansparallel to said beam; a synchronizer for synchronizing a stroke motionof said detecting means with said angle of rotation of the off-centercomponent; and computer means for storing, controlling and evaluating,wherein said detecting means is moved in such a fashion that aseparation, parallel to the beam, between said detecting means and therotating off-center component is kept constant.
 5. The apparatus ofclaim 4, wherein the measured object is a crank shaft.
 6. The apparatusof claim 4, wherein said detecting means comprises a detector having atleast one of a linear photodiode array and a laser scanner.
 7. Theapparatus of claim 6, wherein said detecting means comprises two linearphotodiode arrays and further comprising positioning means to adjust aseparation between said two linear photodiode arrays.
 8. The apparatusof claim 4, further comprising a positioning means to position saiddetecting means within said measurement plane in a direction transverseto said beam.